1. Field of the Invention
The present invention relates to a method for operating a 2-cycle internal combustion engine, more especially to a method of surely igniting air-fuel mixture in a 2-cycle internal combustion engine during even high-speed running ranges.
2. Description of Prior Arts
In a conventional 2-cycle internal combustion engine, the ignition timing is generally retarded during low-speed running ranges with respect to that during the high-speed running ranges so that starting performance such as a stable operation during the low-speed running range may be ensured. On the contrary, while the engine is operated at high speeds, the ignition timing is fixed and rather gradually retarded as the engine speed increases to obtain a maximum output power.
In a typical 2-cycle engine of the type which is designed for speed races, the cylinder volume or the crank volume, port timings (closing and opening timings of an intake and/or exhaust valve) and pressure variations at the intake and the exhaust system are matched with each other to obtain a maximum torque at a set rotational speed of the engine. However, it was impossible to match the above cylinder volume, port timing etc. with each other above the set rotational speed, causing a decrease of the torque.
With consideration why the engine torque is decreased above the set rotational speed, it is found that the amount of newly introduced air-fuel mixture in the combustion chamber at every suction stroke decreases while the amount of residual burnt gases increases since the scavenging operation can not be sufficiently carried out during the exhaust stroke because of no-matching between the pressure variations at the exhaust pipe and the port timings. The cylinder temperature thereby increases over the normal temperature, causing actinations of the mixture such as atomization of the fuel, resolving of the fuel and so on, whereby igniting time and/or velocity of combustion of the mixture is considered to be shorter. In this occasion, the pressure in the combustion chamber reaches the maximum before the piston goes up to the top dead center, so that the piston is pushed downwardly with the result that the output power is reduced, the oil lubrication for the piston is adversely affected and so on. This is proved by our tests in that so-called "Chiri-Chiri" sounds are observed at the high speed operation. Therefore, it will be necessary to retard the ignition timing to restore the combustion of the mixture to its proper operation by such an amount as is equal to the shortened igniting time.